I repotted this Alocasia Polly a few months ago and she seemed so happy! Immediately grew two new leaves and all was well. Last night I noticed these white spots on the underside of the leaves and corresponding dark spots on the top surfaces. I don't see any mites or webs. Does anyone know what this is and how I can treat it?

It may not be mites but it looks like something is sucking the sap out of your leaf. I would sacrifice that leaf, just sit it off and toss it, and treat the rest of the plant with something like Orthene or another good systemic insecticide.